Prolonged feeding of ticks enables the transmission of several infectious agents to the mammalian host. Pathogen transmission by ticks is facilitated by the anti-inflammatory properties of tick saliva. While the extraordinary properties of tick saliva have been known for decades, the signaling mechanisms that lead to a more favorable environment for pathogen transmission remain elusive. The lack of such knowledge is problematic because it precludes the development of novel therapies for preventing infectious diseases. In this proposal, we will understand the complex interplay of a tick salivary protein, a pathogen and the vertebrate immune system. We hypothesize that sialostatin L2 - a tick salivary protein - modulates inflammasome activation and facilitates transmission of the rickettsial pathogen Anaplasma phagocytophilum to a mammalian host. The inflammasome promotes the maturation of inflammatory cytokines and is involved in host defense during infection. Our published and unpublished data show that the inflammasome is important for innate immunity against A. phagocytophilum. We also show that sialostatin L2 inhibits inflammasome activation. We will test our central hypothesis that sialostatin L2 facilitates transmission of the rickettsial pathogen A. phagocytophilum to a mammalian host by pursuing the following aims: (1) we will define signaling pathways that lead to inflammasome activation during A. phagocytophilum infection; and (2) we will characterize how sialostatin L2 inhibits inflammasome activation during tick transmission of A. phagocytophilum. The outcome of this proposal is significantly wide in scope. Ticks, mosquitoes, biting flies, fleas and blood feeding bugs have evolved salivary proteins to modulate host defense. Therefore, our findings may stimulate research into a diverse array of vector-host-pathogen associations resulting in new understandings of pathogenesis and immunity of vector-borne diseases. We envisage that deciphering how arthropod-borne pathogens colonize the mammalian host may lead to novel therapeutics against many arthropod borne diseases.